Inheritance and Disorders MCQ Quiz in मल्याळम - Objective Question with Answer for Inheritance and Disorders - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Key Points

• The term "linkage" describes the physical closeness of genes on a chromosome and their propensity to be passed down in tandem.
• This indicates that genes on a chromosome that are close to one another are more likely to be passed down as a group from one generation to the next.
• This happens because chromosomes, as opposed to genes, are transferred from one generation to the next in their whole form.
• Meiosis involves a mechanism called crossing over, which can separate connected genes and their inheritance.
• Homologous chromosomes exchange genetic material during crossing over, resulting in novel gene combinations in progeny.
• As a result, the gene combinations of the kids differ from those of either parent, which can boost genetic variety within a community.

Concept:

• Mosquito-borne infection diseases are transmitted and spread by the bite of various species of infected mosquitoes.
• For example, chikungunya, dengue, malaria, yellow fever, etc. are mosquito-borne diseases.

Explanation:

Option 1: Thalassemia

• Thalassemia is an autosomal recessive trait that is caused by a mutation of the DNA of the RBCs.
• The mutations caused in the HbA and HbB genes present on chromosome 16 and chromosome 11 respectively are responsible for thalassemia.
• This results in the formation of abnormal haemoglobin molecules, which leads to the destruction of the erythrocytes and anaemia. 

Option 2: Sickle cell anaemia

• Sickle cell anaemia is an autosome-linked recessive trait and the disease is controlled by a single pair of alleles, Hb^A and Hb^S. 
• The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the β-globin chain of the haemoglobin molecules.
• The mutant haemoglobin molecules undergo polymerization under low oxygen tension causing the change in the shape of the RBC from a biconcave disc to an elongated sickle shape.
• In this disease, constantly decrease the number of RBCs as the sickle cells die early.
• When the RBC count is low, the malarial virus cannot attack many RBCs to spread disease.
• The heterozygotic condition of Hb^AHb^S shows increased resistance to malaria.

Option 3: Leukaemia

• Leukaemia is a type of cancer of blood-forming cells that usually begins in the bone marrow and results in the excessive production of abnormal white blood cells. 

Option 4: Pernicious anaemia

• Pernicious anaemia is an autoimmune disorder and results due to a deficiency of vitamin B₁₂.
• The symptoms of Pernicious anaemia include the inability of erythrocytes to maturation, increased size of RBCs, and ineffective RBCs.

Hence, the correct option is (2) Sickle cell anaemia.

Correct Answer: Option 1

Concept:

LINKED GENES:

• ​​The genes that are present on the same chromosome tend to get inherited together. Such genes are referred to as linked genes.
• Linkage refers to the tendency of two or more genes present on the same chromosome to get inherited together.
• Linkage groups refer to all the linked genes in a chromosome. The number of linked genes corresponds to the haploid number of chromosomes in that species.
• The works of T.H. Morgan on Drosophila help us understand the linkage in animals.
• There are two types of linkages depending on the distance of the genes in a chromosome - Complete linkage and Incomplete linkage.
  • Complete linkage:
    • These are the linked genes that are closely placed on a chromosome.
    • As a result of this, they do not undergo crossing over (i.e. do not separate) and get inherited together.
    • These genes are referred to as completely linked genes and the linkage shown by them is called complete linkage.
    • As a result of complete linkage, parental traits are seen in their offspring.
  • Incomplete linkage:
    • These are the genes that are placed distantly from each other on the same chromosome.
    • Due to the distance between them, there are chances of crossing over to take place between these genes. As a result, the genes get separated.
    • These genes are referred to as incompletely linked genes and the linkage shown by them is called incomplete linkage.
    • As a result of crossing over, the recombination of genes takes place. This gives rise to new traits in the offspring.
• The genes that are inherited by offspring from their parents that are either X-linked or Y-linked is called sex-linked inheritance.

Explanation:

• To answer the given question, first, we need to understand T.H. Morgan's experiment on Drosophila.
  • Morgan worked on Drosophila melanogaster.
  • He carried out several dihybrid cross experiments on the fruit fly.
  • These experiments were carried out to study sex-linked genes.
  • One such cross involved, a female with white-bodied and yellow eyes with a male with wild type phenotype of brown-bodied and red eyes.
  • The F₁ progeny so obtained was self-crossed.
  • The F₂ progeny obtained showed a deviation in its phenotypic ratio from that of the Mendelian ratio of 9:3:3:1.
  • Morgan concluded from this observation, that the two genes - body color and eye color - did not segregate independently of each other during gamete formation.
  • These genes were present on the X-chromosome and are hence are sex-linked genes.
  • Morgan stated that when genes in a dihybrid cross are linked, the progeny obtained from such a cross shows a higher proportion of parental combination than the non-parental combination. 
  • This is because of the linkage which does not allow the genes to separate from each other.
• Using the above-given explanation, let us now solve the given question,

ASSERTION: When white-eyed, yellow-bodied Drosophila females were hybridized with red-eyed, brown-bodied males; and F₁ progeny was intercrossed, the F₂ ratio deviated from 9 : 3 : 3: 1.

• ​This statement is true.
• According to the above-mentioned experiment conducted by Morgan on Drosophila, the progeny obtained in the F₂ generation when the F₁ progeny is intercrossed shows a deviation in its phenotypic ratio from that of the Mendelian ratio.
• Normally, the phenotypic ratio of F₂ generation in a dihybrid cross is 9:3:3:1. 
• However, the F₂ generation in the above-mentioned cross showed a deviation from this ratio. This is because the genes are linked and tend to get inherited together.

REASON: When two genes in a dihybrid are on the same chromosome, the proportion of parental gene combinations is much higher than in the non-parental type.

• ​This statement is true.
• In the experiment on Drosophila involving genes that give body color and eye color, they tend to get inherited together.
• This is because the two genes are located on the same chromosome - The X chromosome.
• Due to this, they do not get separated during the crossing over.
• As a result the progeny so obtained shows a higher proportion of parental gene combinations than the non-parental type.
• Thus from the above-given explanation, both the assertion and reason are true and the reason is the correct explanation of the assertion.

So the correct answer is option 1.

The correct answer is option 1.

Concept: 

• Recombination describes the generation of non-parental gene combinations.
• The frequency of recombination between gene pairs on the same chromosome is a measure of the distance between genes and they are mapped based on their position on the chromosome
• Since recombination frequency is directly proportional to the distance between genes, the values are used to locate genes on a chromosome.

• Alfred Sturtevant explained chromosomal mapping on the basis of recombination frequency which is directly proportional to the distance between two genes on the same chromosome.
• It is to be noted that when the distance between two genes increases, the chances of crossing over increase between the two genes present on non-sister chromatids of the homologous chromosomes.
• Crossing over is directly proportional to the recombination.
• The more the crossing over, the more the chances of exchange of genes,s and the more the new recombination formed. Hence, the distance between genes has a direct relationship with the percentage of recombination
• Therefore, the option is the correct answer.
• The rest of the options an irrelevant.

Concept:

• Gene mapping helps to determine the location of genes on the chromosome.
• There are two types of gene mapping - Physical mapping and Genetic linkage mapping.
• In physical mapping distance between two genes is measured in terms of base pairs.
• In genetic linkage mapping distance between two genes is measured in terms of recombination frequency. 

Explanation:

• Genetic linkage maps are based on the fact that how close or far apart are the genes from each other on a chromosome.
• Genes that are found on different chromosomes or are far apart from each other on a chromosome that cannot be inherited together are referred to as unlinked genes.
• Genes that are placed close to each other on a chromosome have a tendency of being inherited together and are called linked genes.
• Linked genes can be placed close to each other and thus will always be inherited together and avoid crossing over.
• Linked genes can also be placed a little farther away from each other on the same chromosome and can get separated during crossing over.
• Crossing over occurs during meiosis I and results in the new recombination of genes.
• This occurs because of the interchange of corresponding segments between non-sister chromatids of homologous chromosomes.
• Thus crossing over gives rise to recombination frequency.
• Recombination frequency is the frequency with which a single crossover takes place between two genes during the pachytene stage of meiosis I.
• Recombination frequency is measured in the unit Centimorgan (cM).
• 1 cM is equal to a 1% chance that two genes will get separated during the crossover.

So, the correct answer is option 3.

The correct answer is ‘X’ or ‘Y’ chromosome of sperm

Explanation:

• The sex of a human embryo is determined by the combination of sex chromosomes it inherits from its parents.
• Humans have two types of sex chromosomes: X and Y.
• Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
• The sperm can contribute either an 'X' or a 'Y' chromosome. If the sperm contributes an 'X' chromosome, the resulting embryo will be female (XX). If the sperm contributes a 'Y' chromosome, the resulting embryo will be male (XY).

The correct answer is: 0.025

Explanation: To find the expected frequency of double crossovers between genes P and R, we will use the formula for the probability of double crossovers, which is the product of the recombination frequencies between adjacent genes. Double crossovers occur when both recombination events happen independently.

Given:

• Recombination frequency between P and Q \((( r_{P-Q} )) \)= 0.18
• Recombination frequency between Q and R \((( r_{Q-R} ))\) = 0.14

The double crossover frequency \((( r_{P-Q} )) \) ×  \((( r_{Q-R} ))\) is: \([ \text{Double crossover frequency} = r_{P-Q} × r_{Q-R} = 0.18 × 0.14 ]\)

• Calculating this: \([ 0.18 × 0.14 = 0.0252 ]\)

Double crossovers are relatively rare events compared to single crossovers. The result 0.025, or 2.5%, indicates the frequency at which double crossovers will be observed in the progeny due to independent recombination events between these genes. In practical terms, understanding double crossover frequency is important for accurate genetic mapping and linkage analysis.

The correct answer is Sex-linked recessive

Concept:

• Sex-linked recessive diseases are typically passed on through the X chromosome. In this case, a carrier female (who has one normal and one affected X chromosome) can pass the affected X chromosome to her male offspring, leading to the expression of the disease since males have only one X chromosome.
• Male progeny that inherit the affected X chromosome from their carrier mother will express the disease because they lack a second X chromosome to mask the effect.
• Examples of sex-linked recessive diseases include hemophilia and color blindness.

Explanation:

• Carrier female: A female who carries one affected X chromosome (heterozygous) and does not show symptoms but can pass the disease to her male offspring.
• Male progeny: Since males have one X and one Y chromosome, inheriting the affected X from the mother leads to the expression of the disease.
• Autosomal dominant/recessive: These conditions affect both males and females and do not exhibit the same pattern of inheritance as sex-linked diseases.

CONCEPT:

• Sickle cell disease and thalassemia are inherited genetic disorders caused by errors in the genes for hemoglobin.
• Sickle cell disease, thalassemia, colour blindness, phenylketonuria, etc. are examples of Mendelian disorders.
• Mendelian disorders are caused by alteration or mutation in a single gene and these are transmitted to the offspring on the same lines.
• Mendelian disorders are mainly sex-linked dominant or recessive and autosomal dominant or recessive.

​EXPLANATION:

Thalassemia:

• Thalassemia is also an autosomal recessive trait that is caused by a mutation of the DNA of the RBCs.
• During thalassemia, a mutation is caused in the HbA and HbB genes present on chromosome 16 and chromosome 11 respectively.
• This mutation results in the formation of abnormal haemoglobin molecules, which leads to the destruction of the erythrocytes and anemia. 
• It also decreases the synthesis of the β-polypeptide chain of haemoglobin.
• Thus, it causes due to a quantitative defect in the globin chain synthesis.
• There are two types of thalassemia, in α - thalassemia, the genes of α-globin have a mutation or abnormality. While in β - thalassemia, the genes of β-globin are abnormal.
• The signs and symptoms of α - thalassemia include, bone complexities, overgrown cheeks, jaws, and forehead, intensely enlarged spleen, etc.
• While the major signs of β - thalassemia include, loss of appetite, jaundice, paleness, tiredness, etc. 

Sickle cell anemia:

• Sickle cell anemia is an autosome-linked recessive trait and the disease is controlled by a single pair of alleles, Hb^A and Hb^S. 
• The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the β-globin chain of the haemoglobin molecules.
• The mutant haemoglobin molecules undergo polymerization under low oxygen tension causing the change in the shape of the RBC from a biconcave disc to an elongated sickle shape.
• Thus, sickle cell anemia is a qualitative defect of the globin chain.

Hence the correct option is (3) Thalassemia is due to less synthesis of globin molecules.

The correct answer is Chromosomal theory of inheritance

Explanation-

• Sutton unified the principles of Mendelian genetics with the knowledge of chromosomal segregation to propose the Chromosomal theory of inheritance.
• This theory states that genes are located on chromosomes, and the behavior of chromosomes during meiosis and fertilization explains the patterns of inheritance observed by Mendel.
• The Chromosomal theory of inheritance provided a molecular basis for understanding Mendel's laws of segregation and independent assortment, as well as the inheritance of traits across generations.
• Walter Sutton, along with Theodor Boveri, independently proposed the Chromosomal theory of inheritance based on observations of cell division and patterns of inheritance.
• Sutton specifically studied grasshoppers and observed that chromosomes behaved similarly to Mendel's hereditary factors (genes) during cell division.
• He noted that chromosomes segregate and assort independently during meiosis, just as Mendel's factors segregate and assort during gamete formation and fertilization.
• It laid the foundation for modern genetics by connecting the principles of heredity with the behavior of chromosomes during cell division and reproduction.

Therefore, the correct answer is Chromosomal theory of inheritance.